A major objective of this research is to elucidate the factors that regulate the growth and differentiation of the small intestinal epithelium. We propose to use artificially reared suckling rats to investigate the influence of hormone and diet on the intestinal growth and differentiation. A known quantity of chemically defined diet will be infused into the stomach of suckling rats. This technique elimates problems of the effect of exogenous hormones originating from maternal milk and the difficulty of quantifying food intake of suckling rats. The procedure of hypophysectomy and hormonal therapy will be used to evaluate the hormones involved in the regulation of the intestinal development. The method of radioimmunoassay will be used to determine the concentration of corticosterone, thyroxine, triiodothyronine, and growth hormone in the plasma of experimental animals and in the diet (if the diet used is supplemented with evaporated milk). We also propose to establish a method to culture epithellial cells in a hormone supplemented, serum-free medium (preliminary results indicate that isolated epithelial cells can be cultured in medium containing 5% FBS for at least 12 days). The regulatory factors involved in vivo will be examined in the epithelial cell cultures. We will examine the effect of these factors, alone or in various combinations, on the plating efficiency, proliferation, differentiation and macromolecular synthesis of the epithelial cell cultures. We also intend to use the cell culture system to examine: (1) ontogenetic development of epithelial cell types; (2) susceptibility of epithelial cells obtained from different ages of animals to hydrocortisone; and (3) regional differences of enzymic patterns in response to hydrocortisone.